Strapping machines or strappers are in widespread use for securing bands of plastic strap around loads. One type of known strapper includes a strapping head and drive mechanism mounted within a frame. A chute is mounted to the frame through which strapping material is fed. The chute includes an assembly for guiding and retaining the strap in the chute so that the strap cannot fall or be pulled inwardly against the load until after a loop of strap has been formed around the load.
The chute is typically constructed in a shape and size suitable to surround and accommodate various shapes and sizes of loads to be strapped. For example, the chute may be generally constructed in a rectangular or square shape since typical loads to be strapped share such a general shape. In one example, the strap guiding and retaining assembly functions to initially maintain the strap in the largest possible loop configuration and to permit the strap to be fed around the load without impinging upon or snagging within the chute.
Prior art chute designs generally employ modular chute components, which are assembled to form the desired chute size and shape. For square and rectangular chutes, the chutes generally include horizontal and vertical chute sections, which are often supported by support beams and connected by corner assemblies. The chute typically is enclosed by a strap retaining and release mechanism of a type well known in the art. It will be appreciated that as loads become larger, so too does the size of the chute to accommodate such larger loads.
In one known strapper, the chute is mounted proximate a work surface and the strapping head is mounted below the work surface to a horizontal portion of the chute. The drive mechanism is also mounted below the work surface proximate the strapping head. In the present example, the drive mechanism urges or feeds the strap through the strapping head and into and around the chute until the strap material returns to the strapping head to form a loop around the load. Essentially, the strap is pushed through the chute by the drive mechanism. After the strap loop has been formed, tension is applied to the strap to constrict the strap loop about the load, and overlapping strap ends are secured by conventional means to create a sealed, tensioned loop around the load.
Generally, there has been a trend to decrease the thickness of the strap. This trend may be due, in part, to the finding that thinner straps (lesser strap gauges) can be used to effectively strap or bundle loads at a lower strap material cost. However, as strap gauge is reduced, the stiffness of the strap is also reduced. This results in strap that may be difficult to push or feed through the strap chute and a greater potential for strap misfeeds, such as short feeds and the like.
To help prevent such misfeeds, it is generally desirable that the strap material exhibit a degree of longitudinal or column stiffness, such that a leading edge of the strap remains generally parallel to the direction of travel (e.g., the strap does not bow or sag downward or inward to an unacceptable degree when traversing along portions of the chute). A degree of column stiffness is also desired such that the strap resists curling, twisting, snagging, or bunching as the strap travels through the chute. However, known straps exhibit only moderate levels of column stiffness due to inherent physical properties of the materials used to form such straps, and the desire to manufacture such straps with minimal thickness and weight.
One example of a strap having improved column stiffness is formed by creating one or more longitudinal ribs in the strap. Such a strap is disclosed in Pearson et al. U.S. Publication No. 2008/0201911, which is incorporated herein by reference. While the ribbed strap of Pearson has been shown to exhibit increased column stiffness, in such ribbed strap, the rib formation is made upon fabrication of the strap, which can increase strap fabrication costs and may increase the size of a spool around which the strap is coiled for an equivalent length of flat strap.
Accordingly, there is a need for a strap with enhanced column stiffness that resists snagging or bunching during travel around the chute of a strapper. Desirably, such a strap would not increase the amount of material required for an equivalent length strap. Also desirably, such a strap is provided in a flat form so as to not increase the spool size for an equivalent length of flat strap or to decrease the total length of strap supplied on typical spool sizes.